LTC4015_15 Datasheet, PDF (32/76 Pages) Linear Technology – Multichemistry Buck Battery Charger Controller with Digital Telemetry System

LTC4015
Operation
sense resistor, R_SNSB, and can be computed in Ω from
BSR • R_SNSB/500. Note that the resistance reported in the
BSR register must be multiplied by the total number of
cells to calculate total battery series resistance. The higher
ICHARGE_BSR (charge current) when a BSR measurement
is requested, the more accurate the BSR measurement will
be. Very low values of ICHARGE_BSR may significantly
impact the accuracy of the BSR measurement. Setting
run_bsr to a 1 will not turn the charger on, if the charger
is suspended or in a termination state, setting run_bsr =
1 results in the BSR measurement request being queued
and run after the soft-start of the next charge cycle.
Battery Charge Voltage Regulation, Constant-Voltage
Once the BATSENS voltage reaches the preset charge volt-
age, the switching charger will reduce its output power,
holding the battery voltage steady. The charge current
will decrease naturally toward zero providing inherently
safe operation by preventing the battery from being over-
charged. Multiple charge voltage settings are available for
final charge voltage selection via the serial port. While
charge voltage trade-offs can be made to preserve battery
life or maximize capacity, it is not possible for the LTC4015
to be set to a charge voltage that is dangerously high or
inconsistent with the battery’s chemistry.
Li-Ion LiFePO₄ Full Capacity Charge Indication (C/x)
and Charger Termination
The battery charge cycle will terminate at the expiration
of a built-in programmable CV termination safety timer
(CV_TIMER). When the voltage on the battery reaches the
programmed charge voltage, the safety timer is started.
After the safety timer expires, charging of the battery will
discontinue and no more current will be delivered. The
safety timer’s default expiration time may be altered via the
serial port. For Li-Ion cells the timer termination feature
cannot be disabled. For LiFePO₄ cells, timer termination
can be disabled by setting MAX_CV_TIME to zero, in this
case, if C/x termination is not enabled, charging will not
terminate.
In addition, by monitoring the charge current and other
states of the system, the LTC4015 determines when the
battery has reached a given state of charge. Specifically,
programmable C/x detection in constant-voltage mode
determines when the charge current has naturally dropped
to a given fraction of its full-scale current. If C/x termination
is enabled the charge cycle will end when C/x is reached,
or when then safety timer expires, whichever occurs first.
C/x termination is disabled by default. The LTC4015 can
optionally be configured via the serial port to generate an
interrupt and terminate charging when the C/x threshold
is reached.
The LTC4015 terminates charging by disabling the switch-
ing controller, when this occurs the SW node goes HI Z.
Li-Ion LiFePO4 Automatic Recharge
After the battery charger terminates, it will remain off,
drawing only a small amount of current from the battery.
If the portable product remains in this state long enough,
the battery will eventually self discharge. To ensure that
the battery is always topped off, a new charge cycle will
automatically begin when the battery voltage falls below
approximately 97.5% of the programmed charge voltage
for Li-Ion and 3.35V/cell for LiFePO₄(3.35V/cell is the
default for LiFePO4_RECHARGE_THRESHOLD in LiFePO₄
programmable mode). The termination safety timer will also
reset back to zero. A new charge cycle will also be initiated
if input power is cycled or if the charger is momentarily
disabled using the serial port (suspend_charger set to 1,
then set to 0).
J.E.I.T.A. Temperature Controlled Charging
For lithium chemistries, a measurement and control
system has been included to enable compliance with the
Japan Electronics and Information Technology Industries
Association guidelines on battery charging. Specifically
a very flexible multi-point temperature-voltage-current
4015f
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For more information www.linear.com/LTC4015